This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the fly wing imaginal disc, a Dpp gradient forms from a localized source, where Dpp is secreted from a stripe of anterior cells that is adjacent to the anterior (A)-posterior (P) compartment boundary. The wing disc consists of a lumen and two layers of cells, a peripodial epithelium and a columnar cell layer. Free diffusion in the lumen can not produce the gradient because the secretory transport domains of Dpp have been fused to GFP, and that fusion GFP fails to form a gradient (Entchev et al., 2000). Several transport mechanisms are proposed involving restricted diffusion, planar transcytosis, cytonemes and argosomes. We are going to address this question by tagging Dpp with PhotoActivetable-GFP, and record the movement of a pulse of Dpp-PAGFP with techniques like FCS or single-particle tracking.